MY98 WRX running with no 02sensor

ratherowna31
Learner Driver
Posts: 3
Joined: Sun Feb 18, 2018 7:51 pm

MY98 WRX running with no 02sensor

Postby ratherowna31 » Thu May 10, 2018 3:44 pm

Ive recently purchased a a 98 WRX with a 3' turbo back and loving every minute of it. We noticed that common hesitation issue from 2000-3500 under moderate throttle but fine under WOT. Replaced fuel filter,cleaned iacv etc. I have read hundreds of forum posts and came to the conclusion the 02 can get very lazy and cause this.
I went and got a new 02 sensor but before installing I decided Id unplug the old one ( located directly behind turbo) and see how it reacted. To my surprise it drove fine with no CEL and basically no hesitation. I left it overnight to cool down and try a cold start where the hesitation is more noticeable. The car performed great with no hesitation. Can anyone help me confirm how many 02 sensors this model has and shed some light why this might be occuring? Thanks

mv75
WRX STi Driver
Posts: 888
Joined: Sat Dec 27, 2014 9:26 pm
Location: Brisbane Northside.

Re: MY98 WRX running with no 02sensor

Postby mv75 » Thu May 10, 2018 6:09 pm

Follow the exhaust and you'll see that there should just be one on that model.

It's just operating in open loop now. If you replace the o2 it should be ok if you got a decent one. The only thing is you may notice a bit more fuel being used. Under wot it's operating in open loop anyway and ignoring the o2.

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Delivan
Impreza 22B Driver
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Joined: Tue Apr 29, 2008 12:18 am
Location: Sitting in the kitchen in Brisbane

Re: MY98 WRX running with no 02sensor

Postby Delivan » Thu May 10, 2018 7:32 pm

My 98 has a later model 2.5 liter engine with a divorced twin down pipe system with an O2 sensor screwed in to block the hole but the wire is cut off the sensor as it is not required. It runs with a Uni Chip piggy back ecu. Had it tuned many years ago when I fitted all the goodies to the engine and it hasn't been tunes since and runs perfectly every time I drive it...Our other GC8 (ver 6 sti) does have an O2 sensor as do our bugs but I think pre 99 didn't use them...
'09 Impreza Charcoal Hatch Auto
'03 WRX Pearl Red Bug Sedan
'02 WRX Silver Bug Wagon
'98 WRX Blue Club Spec Evo 2 with 2.5 lt
'99 WRX White Sti Version 6 with 2.5 lt
'98 Mitsubishi EVO 5 (kept in the basement)

ratherowna31
Learner Driver
Posts: 3
Joined: Sun Feb 18, 2018 7:51 pm

Re: MY98 WRX running with no 02sensor

Postby ratherowna31 » Fri May 11, 2018 1:26 am

mv75 wrote:Follow the exhaust and you'll see that there should just be one on that model.

It's just operating in open loop now. If you replace the o2 it should be ok if you got a decent one. The only thing is you may notice a bit more fuel being used. Under wot it's operating in open loop anyway and ignoring the o2.


Sounds about right as I cant see a post cat o2. Not sure if its decent but its a fuelmiser universal 3 wire from repco.

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